In this article, the authors describe a two-phase inquiry lesson in which students explore the catalytic activity of amylase on starch (Rungruangsa and Panijpan 1979). In the first phase, students' prior knowledge about the reaction is assessed through a set of directed prompts and small-group discussion, then challenged or reinforced as students carry out a laboratory investigation. During the second phase, students design and carry out an experiment to further explore the phenomenon, choosing to study the effect of pH, temperature, or substrate concentration on the kinetics of the starch hydrolysis. (Contains 4 figures.)